When it was introduced, back in 1970, the C-5 Galaxy was the largest plane in the world. It also has the highest operating cost of any US Air Force weapon system, owing to extremely high maintenance demands as well as poor fuel economy. Worse, availability rates routinely hover near 50%. To add insult to injury, the Russians not only built a bigger plane (the AN-124), they sold it off at the end of the Cold War to semi-private operators, turning it into a commercial success whose customer list now includes… NATO.
Meanwhile, the USA still needs long-range, heavy load airlift. The AN-124’s commercial success may get its production line restarted, but the C-5 has no such hope. Boeing’s smaller C-17s cost more than $200 million per plane. That’s about the cost of a 747-8 freighter, for much higher availability rates than the C-5, and a longer lifespan.
What’s the right balance between new C-17s and existing C-5s? The US Air Force believes that the right balance involves keeping some of the larger C-5s, and thought they could save money by upgrading and renewing their avionics (AMP) and engines (RERP). Their hope was that this would eliminate the problems that keep so many C-5s in the hangar, cut down on future maintenance costs, and grow airlift capacity, without adding new planes. Unfortunately, the program experienced major cost growth. In response, the C-5M program wound up being both cut in size, and cut in 2. The C-5A and C-5B/C fleets are now slated for different treatment, which will deliver fewer of the hoped-for benefits, in exchange for lower costs and lower risk.